Casting oven

ABSTRACT

The invention is concerned with an electrically energized casting oven of the crucible type, and one which may be used, for example, for melting precious metals at elevated temperatures of the order of 2,400* F. The oven of the invention includes a coil of resistance steel, or other appropriate resistance material, rather than carbon electrodes, as the heating element.

United States Patent Thiel 151 3,666,919 1 51 May 30, 1972 CASTING OVEN [72] Inventor: Frank M. Thiel, 8828 National Boulevard,

Culver City, Calif. 90230 [22] Filed: June 14, 1971 21 A'ppl. No.1 152,519

219/421, 219/426, 219/521, 266/33 51 1111.0 ..F27b 14/00 58 Field ofSearch ,.219/406, 420, 421,424, 425, 219/426, 427, 434, 521, 536; 13/21, 22, 25; 266/33 [56] References Cited UNITED STATES PATENTS 1,145,455 2/1930 Seaborn ..219/421 2,525,882 10/1950 Ferguson ..13/21 2,708,710 5/1955 De Verter ..219/421 X 2,720,686 10/1955 Higgins et a1... ...2l9/421 UX 2,851,579 9/1958 Pfeifier.... .....219/421 X 2,907,861 10/1959 Melton ..219/521 3,179,731 4/1965 Cash et a1. ..13/21 X 3,430,032 2/1969 Morey ..219/433 Primary Examiner-Volodymyr Y. Mayewsky Attorney-Jessup 8c Beecher [57] ABSTRACT The invention is concerned with an electrically energized casting oven of the crucible type, and one which may be used, for example, for melting precious metals at elevated temperatures of the order of 2,400" F. The oven of the invention includes a coil of resistance steel, or other appropriate resistance material, rather than carbon electrodes, as the heating element.

5 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION The invention finds particular utility in the centrifugal casting of precious metals, such as gold, by the tilt method. In practicing such a method, a metal such as gold is placed in a crucible, and a lost wax flask mold is supported over the mouth of the crucible. The crucible is then heated to an elevated temperature to melt the gold, and the crucible and flask are then rotated on a turntable about a vertical axis. The crucible and flask are pivotally mounted on the turntable, and as the turntable is turned, they tilt and the molten gold from the crucible is forced by centrifugal force into the flask.

Because of the high temperatures involved, especially in casting precious metal, the oven normally used in the prior art to heat the crucible generates its heat by passing an electric current between carbon electrodes. However, it is well known that such an oven is not too satisfactory, primarily because of the rapid deterioration of the carbon electrodes which necessitates their frequent replacement.

The oven of the present invention, however, is constructed to incorporate a coil of electrical resistance material, such as resistance steel, ceramic wire or the like. The coil may be formed, for example, of metal wire or ceramic elements such as are presently marketed by the Kanthal Corporation of Bethel, Connecticut. The elements may be formed to the desired helical shape, .for example, by passing highcurrent therethrough until the particular element becomes pliable, and by then winding the element about a cylindrical mandrel. In operation, for example, temperatures of the order of 2,400 F. and higher may be achieved by passing a current of the order of 300 amperes through the helical element ata voltage. of, for example, 12 volts. Temperatures in excess of 3,000 F. may be achieved by the use of a helix element formed, for example, of Kanthal Super-Ceramic Wire.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The apparatus of FIG. 1 includes, for example, a cabinet 10. Appropriate transformers, drive motors, and other operating components of the apparatus may be mounted within the cabinet. For example, a power transformer for the apparatus may be housed within the cabinet, the transformer being capable, in a particular embodiment, for example, of converting 220 volts AC into l2-24 volts at secondary currents of the order of 300 amperes.

A turntable 12 is rotatably mounted on the top of the cabinet 10, and the turntable may be driven by an electric motor 1 1. supported within the cabinet. When the motor is deenergized, the turntable 12 may be held at a particular angular position by means, for example, of a brake 14. A cylindrical casting oven 16, constructed in accordance with the concepts of the invention, is pivotally mounted on the turntable 12. A clamp 18 is mounted on top of the oven, and the clamp serves to hold a flask mold 20 in position over the mouth of a crucible supported within the oven.

Electric energy for the oven 16 is supplied by electric cables 22 which connect the helical heating element 24 (FIG. 2) of the oven to the secondary of the transformer in the cabinet 10. A disconnect mechanism 26 is mounted on top of the cabinet, and this mechanism is operated by a disconnect lever 28.

When the turntable 12 is stationary, the disconnect 26 serves to connect the cables 22 to the transformer in the cabinet 10 so that current may pass through the heating element 24 to melt the metal in the crucible within the oven 16. When the metal is melted, the lever 28 is operated to cause the disconnect 26 todrsconnect the cables 22 so that the turntable 12 is free to rotate. The turntable 12 is then rotated rapidly by the motor I 1, and the oven 16 and flask 20 are tilted, as a unit, so as to assume a horizontal position. The oven and flask may be tilted, for example, by a hydraulic actuator 29. The gold in the crucible in the center of the oven 16 is then forced into the flask mold 20 by centrifugal action, so that it may be cast into any desired form. A counterweight 31 may be provided at the edge of the turntable 12, as shown. I

The oven 16, as shown in FIG. 2 includes a thin tubular metallic outer wall 50. A cable support 52 may be attached to the outer wall. The heating element 24 is wound as a helical coil which is supported by a tubular member 54 within the tubular outer wall 50. The tubular member 54 may be composed of pieces of appropriate electrical insulating, refractory material. The refractory pieces included members 54a which serve to support the helical heating element, and which project radially inwardly to insulate the crucible (not shown) from the element when it is supported in the oven. The annular space between the tubular member 54 and the tubular outer wall 50 may be filled, for example, with asbestos, or the like. The heating element may be composed of resistance wires or electrically conductive ceramic material, such as described above, so that temperatures in excess of 2,000 F.

may be achieved when an electric current of the order, for example, of 300 amperes is passed through the element. Electrodes 56 connect the cables 22 to the heating element.

The invention provides, therefore, an improved casting oven which incorporates a rugged heating element, and one which is not subject to wear, and need not be replaced during the normal life of the equipment. I

While a particular embodiment of the invention has been shown and described, modifications may be made. It is intended in the following claimsto cover all modifications which fall within the scope of the invention.

What is claimed is:

1. Apparatus for casting precious metal, and the like, including a cylindrical oven member forming a crucible for the metal; a helically wound coil of electrically resistance material surrounding the crucible and responding to electric current to produce elevated temperatures in excess of 2,000 F. in the crucible, thermally insulating material surrounding said heating coil and said crucible, and said oven member being pivotally mounted on a turntable to be tilted about a horizontal axis as the turntable is turned about a vertical axis.

2. The apparatus defined in claim 1, in which the coil is formed of resistance steel.

3. The apparatus defined in claim 1, in which the coil is formed of a ceramic material.

4. The apparatus defined in claim 1, and which includes a clamp affixed to the top of the aforesaid oven to mount a flask mold over the crucible.

5. The apparatus defined in claim 1, and which includes electnc tables extending from an energizing source to the aforesaid coil to energize the coil when the turntable is stationary, and disconnect means for disconnecting the aforesaid tables from the energizing source when the turntable is turned about the aforesaid vertical axis. 

1. Apparatus for casting precious metal, and the like, including a cylindrical oven member forming a crucible for the metal; a helically wound coil of electrically resistance material surrounding the crucible and responding to electric current to produce elevated temperatures in excess of 2,000* F. in the crucible, thermally insulating material surrounding said heating coil and said crucible, and said oven member being pivotally mounted on a turntable to be tilted about a horizontal axis as the turntable is turned about a vertical axis.
 2. The apparatus defined in claim 1, in which the coil is formed of resistance steel.
 3. The apparatus defined in claim 1, in which the coil is formed of a ceramic material.
 4. The apparatus defined in claim 1, and which includes a clamp affixed to tHe top of the aforesaid oven to mount a flask mold over the crucible.
 5. The apparatus defined in claim 1, and which includes electric tables extending from an energizing source to the aforesaid coil to energize the coil when the turntable is stationary, and disconnect means for disconnecting the aforesaid tables from the energizing source when the turntable is turned about the aforesaid vertical axis. 